In human beings, decreased HDL cholesterol levels is one of the most powerful predictors of premature coronary heart disease. A variety of candidate genes may play a role in determining HDL levels. Two of these genes, cholesterol ester transfer protein (CETP) and apoliporpotein A-1, are being examined in the present study to see if there are mutations in these genes which are responsible for marked alteration in HDL levels. Individuals with HDL levels outside 3 standard deviations of the normal (<20 mg.dl or >100 mg.dl) on routine testing in the Cedars- Sinai Reference Laboratory are recruited to participate in the study. To facilitate molecular characterization of mutations in the candidate genes, lymphoblastoid cell lines are being established in the GCRC's Immortalized Cell Line Facility.